Ability to disable alternating face in erc-nicks

[Trevor Arjeski]

As mentioned on #erc, I've been bashing my head against the keyboard trying to
hack up erc-nicks.el, namely `erc-nicks--check-normals', so that the face in the
modeline does not toggle when someone sends back-to-back messages. This causes
the face to alternate between the assigned nick face (from erc-nicks) and the
`erc-default-face'.

Would be nice to just be able to disable this fully and only change the face
when a new speaker sends a message.

I hope that this isn't already possible and I just missed it in my hasty
checking of all configs. Maybe I didn't restart emacs a few times and only
toggled erc-nicks-mode or erc-track-mode a few times...

Thoughts or opinions welcome.